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First Case^ Thin Cylinders, A boiler, or thin cylinder abed.
Fig. 351, tends to tear along the joints a b and cd. Examining a
strip i ''wide we obtain:
Internal load on
I / sa^e strengtrl OI"two sections of
) \ plate (in tension).
; x 2 rx i =ft x 2/x i.
/. ptonsr = f ft
Suppose the plate tends to tear at a ring section as at <?/, then.
/tons x TT rz = /t x 2 TT r x t.
From this we find that
Stress on longitudinal section =
and stress on transverse section = \
so there is no fear of a boiler bursting at a cross seam. The
above supposes the boiler plate to be of uniform construction
throughout. But as the seams, whether welded or riveted, are
much weaker than the * solid ' plate, a multiplier (?/) must be in-
troduced on the right side of the equation to reduce the quantity
and shew the strength at the joint. Then :
strength of joint
strength of solid plate
efficiency per cent = ğ7 x 100
) = efficiency =
For lap welded joints,
For single riveted joints,
For double riveted joints, 77 =
________________ jm^ tj .* >roughly
For electric welded joints, 77 = -85 ) (See p. 755.)
and the formula for boilenor pipe strength becomes
Example 6. A copper steam pipe 12" dia. is to resist ağ internal
pressure of 160 Ibs. per sq. in. Find its thickness, if ^ for the brazed
joint = 80%
From above formula - - x 6 == 2 x /x *8 .*. / ğ '267 ins.